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/*
* gsbase.c, a gsbase test
* Copyright (c) 2014 Andy Lutomirski
* GPL v2
*/
#include <stdio.h>
#include <stdbool.h>
#include <sys/syscall.h>
#include <unistd.h>
#include <err.h>
#include <sys/user.h>
#include <asm/prctl.h>
#include <sys/prctl.h>
#include <sys/mman.h>
#ifndef __x86_64__
# error This test is 64-bit only
#endif
static unsigned char *testptr, *testptr2;
static unsigned char read_gs_testvals(void)
{
unsigned char ret;
asm volatile ("movb %%gs:%1, %0" : "=r" (ret) : "m" (*testptr));
return ret;
}
int main()
{
int errors = 0;
testptr = mmap((void *)0x200000000UL, 1, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_FIXED | MAP_ANONYMOUS, -1, 0);
if (testptr == MAP_FAILED)
err(1, "mmap");
testptr2 = mmap((void *)0x300000000UL, 1, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_FIXED | MAP_ANONYMOUS, -1, 0);
if (testptr2 == MAP_FAILED)
err(1, "mmap");
*testptr = 0;
*testptr2 = 1;
if (syscall(SYS_arch_prctl, ARCH_SET_GS,
(unsigned long)testptr2 - (unsigned long)testptr) != 0)
err(1, "ARCH_SET_GS");
usleep(100);
if (read_gs_testvals() == 1) {
printf("[OK]\tARCH_SET_GS worked\n");
} else {
printf("[FAIL]\tARCH_SET_GS failed\n");
errors++;
}
asm volatile ("mov %0,%%gs" : : "r" (0));
if (read_gs_testvals() == 0) {
printf("[OK]\tWriting 0 to gs worked\n");
} else {
printf("[FAIL]\tWriting 0 to gs failed\n");
errors++;
}
usleep(100);
if (read_gs_testvals() == 0) {
printf("[OK]\tgsbase is still zero\n");
} else {
printf("[FAIL]\tgsbase reset itself to 1\n");
errors++;
}
return errors == 0 ? 0 : 1;
}
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